That's the ethic of the hustler—the guy who slogs through his day job at Staples and spends nights delivering Chinese food. Sure, he's an aspiring artist looking to get signed by a label, but he knows an important rule: Pride doesn't pay the bills.

It's a common ethos in athletes, who—contrary to what some might think—don't exit the womb with pro contracts in hand. Most pros came from some more or less humble beginning and spent many a late night and early morning getting to where they are now.

There's a select few, however, who continue to actively pursue new, non-sports related avenues of income, while still playing the game that made them millionaires.

The following are the athletes who are still in the game and still hustling for cash on the side.

Peyton Manning: Pizza Baron

Image via @BeltiSchool

The Hustle: Weeks before Colorado legalized recreational marijuana use in 2012, Peyton Manning made what's known in sports as "a heads up play" and purchased 21 Papa John's pizza stores in the Denver area.

I'll spare you a "rolling in the dough" pun, but I must add that moving into the pizza business is paying dividends for Peyton.

As of this fall, Manning-owned Papa John's shops have reported increases in sales of up to 25 percent annually—a bump that has yet to reverberate into non-Manning owned Papa John's store in the area.

Vernon Davis: Juice Monger

Image via @VernonDavis85

The Hustle: 49ers tight end Vernon Davis recently took over a Jamba Juice in Santa Clara, Calif.

A health nut with a love for pumping iron, Davis says he bought into Jamba Juice because the business and he share the same healthy philosophy on life. They also presumably share an interest for making money, which comes in by the truck when you're selling kale-boosted fruit gravy to Californians.

Davis says one his favorite drinks is the "Peach Pleasure" smoothie. Relish that knowledge.

Carmelo Anthony: Record Producer

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The Hustle: Carmelo Anthony owns Krossover Entertainment—a record label with several minor hip hop artists to its name.

Anthony began plotting the creation of his own record label sometime in the mid-2000's, ostensibly as a vehicle to help promote the aspiring musical careers of his friends. The result was Krossover, a small label including Cassidy (probably the most well known artist), Diego Ca$h and other hip hop artists.

It's unclear how much time Melo spends on developing his label, as it appears to be more of a pet project/creative outlet than a money-making venture.

Brian Hartline: Convenience Store Owner

The Hustle: After signing a $31 million contract extension with the Dolphins, wideout Brian Hartline continued working at a drive-thru convenience store.

There's not many times when a millionaire chooses to take orders at the drive-thru window, but that's exactly what Hartline did after the 2012-13 season. During an interview with Dan LeBatard, the wideout claimed he opened a convenience store with one of his friends during the offseason.

Well, if this whole professional football career thing doesn't pan out, Hartline and his buddy can always live out Clerks under the dingy halogen lights of the Quick Stop.

Cam Newton: Fashionista

Screenshot via @lemsanders

The Hustle: Cam Newton has teamed up with Belk to create "MADE Cam Newton," a clothing line inspired by the Carolina Panthers quarterback.

Newton doesn't "actually sketch" the clothing designs for the articles in his collection, but he provides his "input" on the clothing's patterns and colors. In other words, he says, "Yes. That. Make them. Buy that," and collects his checks.

Travis Daniels: Barbershop Owner

Screenshot via CNN.com

The Hustle: NFL free agent Travis Daniels is the primary investor in Kutz Remix, a barbershop in Suwanee, Ga.

When they were kids, Travis promised his brother Sheppard that he'd help him open his own barbershop one day. The former Chiefs cornerback followed through on that promise in 2011, investing in Kutz Remix—a next-level barbershop boasting plasma screens and DJ Booth spinning tunes throughout business hours.

How the business fares today is unknown, but considering Travis is now a 31-year-old free agent in the league, he may be glad he invested some of his contract money in a business people will always need.

Maria Sharapova: Sugar Peddler

Screenshot via @MidwestSports

The Hustle: Maria Sharapova has launched "Sugarpova"—her own, awfully named brand of candy.

After starting her own candy company, the No. 3 ranked women's tennis player in the world took her marketing to the wild heights by announcing her wish to change her name to "Sugarpova" for the duration of the U.S. Open.

Sharapova eventually nixed the name change, presumably after realizing she was about to abandon her personal identity in the name of hyping up a candy company—or because she realized the USTA wouldn't allow it in the first place. Either/or.

Retiree Honorable Mention: Magic Johnson, Franchise Master

The Hustle: An entrepreneur with many investments, Magic Johnson's fortunes have grown even larger since retiring.

The list of Magic's business ventures to date is nearly unending, but the investments that brought him to the level of wealth he currently enjoys today began with theaters and coffee.

In the mid-'90s, Magic opened a line of Magic Johnson Theaters at the Baldwin Hills Crenshaw Plaza. His venues were a hit, and their success opened the door for his next investment: Starbucks Coffee.

Until 2010, Magic was the only Starbucks franchise operator in the world, due to the company's strict, anti-franchising policy. He owned 105 Starbucks locations, which he sold back to the company in 2010. I imagine he was sitting rather flush after that divestment.